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Posts in Networking
Deploying Highly Available Virtual Interfaces With Keepalived
I recently played around with keepalived, and documented my experiences in an article titled Deploying Highly Available Virtual Interfaces With Keepalived. If you are interested in deploying highly available Linux routers, or just looking to failover IP addresses between servers, you may find the article useful.
$ read more →Installing a tftp server on CentOS and Fedora Linux servers
While upgrading the firmware on several network devices this past weekend, I needed to bring up a tftp server so the clients could retrieve the firmware image. I had a Fedora host readily available, so getting tftp up and working was super easy. Before configuring the server, I ran yum to install the tftp-server package: Once the package was installed, I set "disable" to no in /etc/xinetd.d/tftp (I also disabled the server as soon as I was done using it): After the server was configured, I restarted xinetd and everything worked like a champ. If you encounter any issues tftp'ing files, there are a couple of things you can do to troubleshoot the source of the problem: Add one or more "-v" (verbose output) directives to the /etc/xinetd.d/tftp "server_args" line Start the tftp client by hand, and set the "verbose" and "trace" options Fire up tethereal to decode the TFTP requests and responses While tftp is completely insecure, it's still one of those protocols that we have to live with.
$ read more →How The ISC DHCP Server Derives Host Names
Like most DHCP implementations, the ISC DHCP server supports sending host names in response to a DHCP DISCOVERY message. The host name is sent when DHCP option 12 is requested by the client, and the name is derived from one of two locations: The ISC DHCP server will look up the IP address in DNS The server will use an administratively defined host name To configure ISC DHCP to set the host-name option based on DNS data, you can set the "get-lease-hostnames" directive to true: get-lease-hostnames true; If you are unable to use DNS to derive the host name, you are still in luck. You can specify the name to assign to the client in a host block: In the example above, the host name "thecrue.prefetch.net" will be assigned to the client with mac address 00:24:8c:4e:07:f6. If you have a large number of hosts and you want to use the name that is attached to the host directive, you can use the "use-host-decl-names" directive…
$ read more →Building ISC DHCP 4.X on Solaris hosts
I attempted to upgrade my ISC DHCP installation to dhcp-4.1.1b1 this past weekend, and ran into the following configure error: Th config.log had a number of errors similar to the following: Which are due to missing system headers. I reviewed the list of packages that were installed, and sure enough SUNWhea (this package contains the various header files) was missing. I installed this package as well as a number of others: Any everything compiled and installed perfectly.
$ read more →How does crossbow deal with MAC address conflicts?
When I gave my presentation on Solaris network virtualization a few months back, one of the folks in the audience asked me how Crossbow deals with duplicate MAC detection. I didn't have a solid answer for the gentlemen that asked, but thanks to Nicolas Droux from Solaris kernel engineering, now I do. Here is what Nicolas had to say about this topic on the network-discuss mailing list: "When a VNIC is created we have checks in place to ensure that the address doesn't conflict with another MAC address defined on top of the same underlying NIC. When the MAC address is generated randomly, and the generated MAC address conflicts with another VNIC, we currently fail the whole operation…
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